1. Field of the Invention
The present invention relates to the generation of graphic symbols and characters for presentation on a Cathode Ray Tube (CRT).
2. Description of the Prior Art
In many Cathode Ray Tube applications, the presentation of graphic symbols and characters with low distortion particularly at the beginning of a line is of prime importance. Radar systems and radar collision avoidance systems are examples of applications where high quality graphic symbols and characters are needed.
Most CRT systems use magnetic deflection of the electron beam to draw graphic symbols. When deflection voltage is applied to the deflection coils of the magnetic deflection system, the beginning of the graphic symbol being drawn on the face of the CRT is distorted due to the inherent inductive lag of the deflection coils while the deflection circuit is charging.
Previous solutions have employed an impulse or step voltage across the deflection coils slightly before the start of a graphic symbol in an effort to reduce distortion. Other schemes have included adding a fixed bias across the deflection coils. With a fixed bias arrangement, the distorted beginning portion of a graphics symbol begins before the desired x--y start point and the electron beam is kept blanked for a predetermined period of time until the desired x--y start point is reached. The disadvantage of a fixed bias arrangement is that additional circuitry is required to detect when the desired x--y start point has been reached or the fixed bias must change as a function of the CRT range scale of the drawing rate of the graphics symbol.